1. Field of Invention
The present invention relates to bullets for obtaining cores or samples from formations adjacent to well bores.
2. Description of Prior Art
In petroleum exploration, it is desirable to determine the nature and composition of rock formations at various depths in a well bore hole. One way has been the use of sampling bullets. Typically, a number of such bullets are mounted with associated explosive charges on a sampling tool for movement through the well bore.
At a selected depth, the charge for one or more of the detonating charges for the bullets is ignited, firing the bullet into the rock formation. The bullet is provided with a central opening or passage which gathers and retains a core or sample of the formation rock as the bullet enters. The bullet enters the rock a distance of about one inch but is kept connected to the tool by wire cable(s). When the tool is moved away from the formation, the bullet is extracted from the formation and is suspended by retrieval cable(s) attached to the tool. After all bullets have been fired, the cores in them are transported by the tool to the surface for geological analysis.
After the sampling tool with its fired, suspended bullets is transported to the surface, the formation cores are removed from the bullets and transported to a suitable facility for geological examination. The bullets may be reused a number of times simply by inserting new firing charges into the sampling tool and properly positioning the bullets within the tool in readiness for subsequent firing.
After the formation cores have been separated from the bullets, they are of course subject to considerable degradation and contamination by the harsh environment of the field. It is desirable, therefore, to provide the formation cores with adequate protection from contamination and degradation.
In many cases, the formation being sampled is relatively unconsolidated and the formation cores tend to fragment upon separation thereof from the core sampling bullets. It is also desirable to maintain unconsolidated core samples intact while removing the samples from the sampling bullets and during transportation of the core samples to a suitable laboratory facility.
It is also desirable to insure that geologists are made aware of the particular orientation of the formation core samples so that the physical character of the formation being sampled may be more readily apparent.